The present invention relates to a motor driver suitable for driving a brush-less dc motor used in an air conditioner, a water heater equipped with a combustion fan motor, an air cleaner, and information apparatuses such as a copying machine and a printer. More particularly, it relates to a motor driver that feeds motor driving coils with an alternating current consecutively varying, more preferably an approx. sine-wave current. The flow of the ac makes a phase difference generally zero between a phase of the back electromotive forces induced in those coils and a phase of the ac running through those coils. As a result, a motor of lower torque ripples, fewer vibrations, and lower noises is obtainable.
DC brushless motors have been widely used as driving motors built in, e.g., an air conditioner and an information apparatus including a copying machine, a printer and the like because of the advantages of the motors such as a long service-life, high reliability, and easiness of speed control.
FIG. 17 is a circuit diagram of a conventional motor driver. FIG. 18 shows waveforms at respective sections of the motor driver with respect to a rotating angle (electrical angle) of the motor.
As shown in FIG. 17, a driver of a brushless DC motor (hereinafter simply referred to as a motor), in general, detects a rotor position with a plurality of position detectors 901, 903 and 905 comprising a Hall effect device. Three-phase distributor 890 receives position signals Hu, Hv and Hw, and outputs three-phase distribution signals UH0, UL0, VH0, VLO, WH0, and WLO to pulse-width modulator (PWM modulator) 840, where those signals are modulated into signals having a pulse width responsive to signal S set by speed setter 860. Modulator 840 outputs signals which control, via gate driver 830, six switches 821-826 forming power-feeder 820 to be sequentially turned ON or OFF. The power supplied to three-phase coils 811, 813 and 815 is thus switched in sequence responsive to a rotor position like signals U, V and W as shown in FIG. 18, so that the motor is spun.
A voltagexe2x80x94applied between a coil end of each one of respective phase coils and neutral point Nxe2x80x94shapes in a rectangular waveform, thus changing a current in the respective phase coils causes sharp ON-OFF switches responsive to the rectangular waveform signals. As a result, coils are vibrated, thus mechanical noises and electrical noises are produced. The switching frequency of the respective phases generates torque ripples, which vibrate the apparatus employing the motor, and the vibrations resonate the apparatus, so that noises are produced.
A motor driver, driving the motor-driving-coils of respective phases with a driving waveform in a sine-wave, is well known to lower the foregoing noises and electrical noises. This kind of motors are disclosed in Japanese Patent Application Non-Examined Publication No. H06-233583, H06-233584, H06-233585, and Japanese Patent No. 2658085. Those motor drivers disclosed in the foregoing publications use a detected output from a detecting element which detects major magnetic-field for driving, and an address signal formed of the output of the detecting element, whereby a driving waveform stored in a memory is read out for driving the motor.
In the conventional motor driver discussed above, however, the driving waveform with respect to a rotational position of the rotor, namely, a voltage waveform applied to the coils of respective phases, is uniquely determined by digital-signal data stored in the memory discussed above. Thus, in the case where the driver drives a motor having a rather large inductance, e.g., a stator iron core is wounded with coils, a phase delay of current of respective phases with respect to the voltages applied to the respective phases becomes larger when the driving waveform is applied to the respective phases. Such a delay in the respective phase currents enlarges a phase difference between the back electromotive force (BEMF) induced in the respective phases and the phase current. As a result, the torque of the motor is reduced, namely, efficiency of the motor is lowered.
In general, the torque of motors is approx. proportionate to cos. xcfx86, where xcfx86 is a phase difference between the BEMF induced in respective phases and the phase current. In other words, when the phase difference between the phase current and the BEMF becomes zero (xcfx86=0), the torque of the motor can be optimally supplied. However, an inductance component of driving coils positively generates a phase delay in the phase current, so that the foregoing phase difference is produced. This phase delay is taken into consideration in advance, so that the mounting position of a position detector for the rotor is mechanically shifted such that each voltage applied to respective phases is advanced. This method is conceivable; however, an amount of the phase delay in current is not constant but varies depending on a load or an rpm. Thus this method is able to produce an optimized efficiency only at a specific load.
As discussed above, the phase delay of phase current varies depending on the condition of a motor in use such as a load or an rpm, or the properties of the motor per se such as a BEMF, an inductance, and electrical time constant. Therefore, the foregoing phase difference cannot always stay at zero for driving the motor at the optimum efficiency.
The conventional motor driver discussed above, however, requires a memory storing a predetermined driving waveform and a digital-analog (D/A) converter which reads out the driving waveform (digital signal) before converting the digital signal into an analog signal for driving the motor. The conventional motor driver is thus equipped with a complicated circuit.
The present invention addresses the problems discussed above and aims to provide a motor driver that can drive a motor at an optimal efficiency in any conditions with lower torque ripples, fewer vibrations, and lower noises. This motor driver is simply structured, where the driving coils of the respective phases are fed with an ac in approx. sine-waveform, and the phase difference between the ac and the back electromotive force (BEMF) induced in those coils is kept always at nearly zero.
The motor driver comprises the following elements:
(a) driving coils for three phases;
(b) a dc power supply disposed between a first feeder line and a second feeder line;
(c) a driving wave generator for generating driving waves at intervals of one cycle in electrical angles corresponding to respective phase-coils;
(d) a phase advancing controller for controlling a phase of a driving waveform; and
(e) a power feeder for driving respective coils with an alternating current consecutively changing, by coupling the respective coils to a first feeder line or a second feeder line based on a modulated signal produced by modulating a pulse width of the driving waveform.
To be more specific about some elements discussed above, the power feeder can achieve at least the following two coupling statuses:
a first coupling status: a second phase is coupled to the first feeder line, and a first and a third phases are coupled to the second feeder line, and
a second coupling status: the first and the second phases are coupled to the first feeder line, and the third phase is coupled to the second feeder line.
The phase advancing controller compares a value of common current running through the first or the second feeder line in the first coupling status with that of the second coupling status, and controls a phase of the driving waveform such that the common current values of the respective coupling statuses become approx. the same in the vicinity of the zero-cross of the BEMF induced in the first phase coil. This phase control of the driving waveform by the phase advancing controller allows the phases of BEMFs of the respective phase coils to be approx. matched with the phases of the ac running through those coils.
The structure discussed above allows the motor driver of the present invention to drive a motor efficiently with less torque ripples, fewer vibrations and lower noises.
The apparatuses of the present invention employ this motor driver in their fan motors.
The apparatuses of the present invention employ this motor driver in their driving systems.
Since those apparatuses of the present invention employ this motor driver, the apparatuses work efficiently with fewer vibrations and lower noises.